shhyou

-- L = {0^n 1^n | n \in N}

match :: String -> Bool
match s = case trace s of
            Just [] -> True
            _       -> False
          where trace :: String -> Maybe String
                trace ('0':xs) = do
                  remainString <- trace xs
                  (case remainString of

shhyou

-- The CPS-transformed version of match.
-- https://gist.github.com/suhorng/5204442

match' :: String -> Bool
match' s = trace s null
           where trace :: String -> (String -> Bool) -> Bool
                 trace ('0':xs) k = trace xs $ \remainString ->
                                      case remainString of
                                        '1':xs' -> k xs'
                                        _       -> False

shhyou

-- Defunctionalizing match' -- we obtain a 2-state push-down automaton!
-- 1) https://gist.github.com/suhorng/5204442
-- 2) https://gist.github.com/suhorng/5204636

data Cont = Cont0
          | Cont1 Cont

match'' :: String -> Bool
match'' s = trace s Cont0
            where trace :: String -> Cont -> Bool

shhyou

{-
  The original evaluator to be transformed.
  See A Functional Correspondence between Evaluators and Abstract Machines, by O. Danvy
  www.brics.dk/RS/03/13/BRICS-RS-03-13.pdf
-}
data Value = Var String
           | Lambda String Expr

data Expr = Val Value
          | Ap Expr Expr

shhyou

{-
  The abstract machine obtained by transforming
  the original direct evaluator.

  Previous codes: https://gist.github.com/suhorng/5355222
-}

data Value = Var String
           | Lambda String Code

shhyou

#include <cstdio>
#include <cstring>
#include <algorithm>

char l_exist[10000], r_exist[10000];
int n, m, val[10000], seq[10000];

int main() {
  int i, j, k, diff, ans = 0;
	scanf("%d", &n);

shhyou

import pygame
import sys # exit
import random # randint
from collections import deque

def new_food(snake, surface):
  newfood = (random.randint(0, 80)*10, random.randint(0, 60)*10)
  # the food shouldn't appear inside the body of the snake or at where we show the score
  while newfood in snake or newfood[1] >= 550:
    newfood = (random.randint(0, 80)*10, random.randint(0, 60)*10)

shhyou

(define Y
  (lambda (f)
    (let [(A (lambda (x) (f (lambda (y) ((x x) y)))))]
      (A A))))

(define (factF self)
  (lambda (n)
    (if (= n 0)
      1
      (* n (self (- n 1))))))

shhyou

Essentials of Programming Langauges 1e
Daniel P. Friedman, Mitchell Wand, and Christopher T. Haynes

Chapter 1 Tools for Symbolic Programming
1.1 Simple Expressions
1.2 Data Types
1.3 Procedures
1.4 Summary

Chapter 2 Induction, Recursion, and Scope

shhyou

Essentials of Programming Langauges 3e
Daniel P. Friedman and Mitchell Wand

Chapter 1 Inductive Sets of Data
1.1 Recursively Specified Data
1.2 Deriving Recursive Programs
1.3 Auxiliary Procedures and Context Arguments
1.4 Exercises

Chapter 2 Data Abstraction